Update on Lake Superior Outflows and Expected Conditions - June 2023
Anglers and other users of the St. Marys Rapids, please be advised that the gate setting of the Compensating Works at the head of the St. Marys Rapids will be maintained at the current setting equivalent to approximately eight gates fully open. The St. Marys Rapids flow will remain at approximately 1,200 m3 /s for the month of June.
Low-lying areas of Whitefish Island including recreational trails are currently flooded and portions of the Island have been closed by Batchewana First Nation. Users are encouraged to use extreme caution. The Board advises that even higher flows in the St. Marys Rapids are possible in the coming months, which may increase the level of flooding on Whitefish Island.
The International Lake Superior Board of Control (Board) received approval from the International Joint Commission (IJC) to temporarily deviate from Regulation Plan 2012 through November 2023. This deviation strategy is similar to the strategy employed in 2019. Over the next several months, the Board will continue to adjust the gate settings at the Compensating Works in order to offset the flow limitations caused by repairs and maintenance at the hydropower plants. The total amount of water released through the St. Marys River will be approximately equal to the flow prescribed by Plan 2012 and the deviation strategy will have almost no cumulative impact on the water levels of Lake Superior and Lake Michigan-Huron yet will provide reduced fluctuations in flows and water levels in the St. Marys Rapids, directly downstream of the Compensating Works.
The Board expects the total St. Marys River flow in June to be 2,950 m3 /s (104,200 cfs) which is 150 m3 /s (5,300 cfs) less than the flow prescribed by Regulation Plan 2012. Actual hour-to-hour and day-to-day flows may vary depending on hydrologic conditions, as well as variations in flow from the hydropower plants.
Water level changes over the month of May
- Lake Superior rose by 8 cm (3.1 in) last month, while the seasonal long-term average rise is 10 cm (3.9 in) in May.
- Lake Michigan-Huron rose by 6 cm (2.4 in) last month, while the seasonal long-term average rise is 9 cm (3.5 in) in May.
- Water levels have been relatively stable in the latter half of May, after rising rapidly in April and early May because of rapid snowmelt and significant rainfall.
Water levels as of the beginning of June
- At the beginning of June, the lake-wide average water level of Lake Superior is 26 cm (10.2 in) above the seasonal long-term average (1918-2022) and 14 cm (5.5 in) above the level of a year ago.
- At the beginning of June, the lake-wide average water level of Lake Michigan-Huron is 15 cm (5.9 in) above average and 11 cm (4.3 in) below the level of a year ago.
The seasonal average pattern is for water levels of Lake Superior and Lake Michigan-Huron to continue to rise in June. On average, Lake Superior and Lake Michigan-Huron reach their seasonal peaks in July or August. Depending on the weather and water supply conditions during the next month,
- Lake Superior may rise by as much as 13 cm (5.1 cm). If conditions are dry, Lake Superior may begin its seasonal decline in June.
- Lake Michigan-Huron may rise by as much as 14 cm (5.5 in). If conditions are dry, Lake Michigan-Huron may remain stable in June
The International Lake Superior Board of Control is responsible for managing the control works on the St. Marys River and regulating the outflow from Lake Superior into Lake Michigan-Huron. Under any outflow regulation plan, the ability to regulate the flow through the St. Marys River does not mean that full control of the water levels of Lake Superior and Lake Michigan-Huron is possible. This is because the major factors affecting water supply to the Great Lakes (i.e. precipitation, evaporation, and runoff) cannot be controlled, and are difficult to accurately predict. Outflow management cannot eliminate the risk of extreme water levels from occurring during periods of severe weather and water supply conditions. Additional information can be found at the Board’s homepage: https://ijc.org/en/lsbc or on Facebook at: https://www.facebook.com/InternationalLakeSuperiorBoardOfControl